RE: SPFv1 is already extensible

Stuart D. Gathman wrote:
> As someone else has pointed out, SPFv1 is already completely extensible in 
> any way desired by means of the 'exists' mechanism and a custom DNS 
> server.
Excellent point! However, I'd like to make sure we aren't confusing "flexibile" 
with "extensible". Are there (extended) mechanisms which cannot be expressed as 
an 'exists' mechanism? I can't think of any, but then I'm a bit out of it right 
now.

Michael R. Brumm